Laughter plays an important social function, signalling to the joke-teller that we share their perspective on the world and that we recognise their witty intent. Sometimes these guffaws arise spontaneously from genuine mirth, other times it’s more strategic: we ingratiate ourselves with the joke-teller by letting them know we appreciate their humour. But actually most of our laughter isn’t caused by jokes. We laugh much more often when we’re the one doing the talking, but again we’re using this ‘voluntary laughter’ as a social device, conveying feelings of closeness and playfulness to the people we’re with.